WHITEFISH OF THE LAKE OF GENEVA 



r 



which suffice for a superficial determination but 

 are not sufficient to complete the picture. This we 

 can obtain by catching these little animals directly, 

 whole and intact, in the water where the fishes feed 



upon them. We 

 know how to go 

 about this — I have 

 already indicated 

 the method at the 

 beginning of this 

 book — we use a 

 sfl V^^r-^-' / *\ plankton net. 



From my boat I 

 draw this apparatus 

 for a few moments 

 through the waters 

 of the lake, then 

 bring it up and ex- 

 amine the contents. 

 There I find, active 

 and moving in all 

 directions, these 

 tiny crustaceans 

 whose fate it is al- 

 ways to be the prey 

 of greater creatures. 

 I see them swim- 

 ming, displaying all 

 the details of their 

 structure. And so 

 I understand what 

 happens in Nature. In their accustomed state they 

 swim in the lake water as they do before me in that 

 of the receiver; they are suspended in it, part of the 

 plankton, and so float throughout their lives, peopling 

 the waters with their hosts, ready to be devoured by 

 those who have only to open their mouths and take 

 them. The food offers itself, and the story of manna 



i 7 6 



Fig. 33. — Cyclops (genus Cyclops), plank- 

 tonic crustacean of the order Copepoda. 

 There are many species, the largest of 

 which are hardly more than 2 to 3 milli- 

 metres in length. 



